Print hammer module



Feb. 11, 1969 F, DAL N 3,426,675

PRINT HAMMER MODULE Filed March 17, i967 W |O l4 I6 32 5 1 52 g .5 II |2\ H 30 22 CONTROL CIRCUIT INVENTOR.

JOHN E DALTON A TTORNE Y United States Patent 3,426,675 PRINT HAMMER MODULE John F. Dalton, Worcester, Mass, assignor, by mesne assignments, to Mohawk Data Sciences Corporation, East Herkimer, N.Y., a corporation of New York Filed Mar. 17, 1967, Ser. No. 623, 873

US. Cl. 101-93 6 Claims Int. Cl. B41j 9/10 ABSTRACT OF THE DISCLOSURE A free-flight print hammer is propelled against a print surface by a pivoted actuating arm acted upon at its center of percussion by a solenoid. The pole piece of the solenoid serves as a stationary stop to arrest the travel of the atcuating arm before the hammer reaches the print surface, thus producing a true ballistic printing action. Since the pole piece acts, both in attracting and in arresting the arm, substantially on the arms center of percussion, printing is achieved with minimum expenditure of energy and noise generation. Resilient washers are used to damp the impact produced upon return of the arm to its rest position stop.

Background of the invention This invention relates to print hammer modules and more particularly to an actuating mechanism for print hammers of the free flight or ballistic type.

I have found that in the usual type of free-flight print hammer mechanism some type of solenoid mechanism is employed for driving the hammer against the print surface when it is desired to print a character. Generally, the hammer is spring biased to a non-printing position and the solenoid is used to generate a force which momentarily overcomes the spring bias and sends the hammer into free flight toward the print surface. I have found the prior art mechanism to be less than satisfactory from the standpoint of energy consumption, noise level and overall size of the unit.

Objects and summary of the invention It is an object of the present invention to provide an improved print hammer module which operates with reduced energy consumption, produces less noise and is more compact than prior art devices of which I am aware.

Another object is to provide an actuating mechanism for driving a free flight print hammer, which mechanism operates to damp out a significant portion of the extraneous mechanical oscillations generated during the printing operation and which therefore consumes less energy, reducing the noise level and permitting operation at repetition rates up to 100 cycles per second.

In accordance with the principles of the invention, a free-flight print hammer is propelled against a print surface by a pivotable actuating arm which is driven by a solenoid and which is arrested prior to the time the print hammer reaches the print surface. The solenoid acts upon the center of percussion of the pivotable actuating arm and, further, includes a pole piece which functions as a stop to arrest the travel of the arm. This arresting means also acts upon the center of percussion of the arm.

As is known, a force acting on the center of percussion of a body and at right angles to a line joining the body to a pivot center or center of oscillation imparts pure rotational movement to the body with respect to the pivot center. As is further known, particularly to golfers and baseball players, an object striking a body at its center of percussion produces a good deal less noise on impact since a maximum amount of energy is transferred between the two bodies, minimizing the level of residual energy available for producing noise. In applying these principles to a mechanism for driving a print hammer in the manner described in detail hereinafter. I have found that the usual amount of striking force required at the print surface can be generated at lower solenoid power consumption levels and that much quieter operation is obtained. In addition, the module is very compact and low in cost.

Other objects, features and advantages of my invention will be apparent from the preferred embodiment thereof hereinafter set forth in the detailed description and illustrated in the accompanying drawings.

Brie) description of the drawings FIG. 1 is a side elevational view of a preferred embodiment of my invention. In addition to the hammer module, portions of the print drum, ink ribbon and document are also shown.

FIG. 2 is an enlarged view of a portion of FIG. 1 showing the means employed to damp the impact of the actuating arm upon its return to home position after a print operation.

Detailed description Referring to FIG. 1, there is shown a portion of a print drum 10, ink ribbon 14 and document 16. Drum 10 rotates continuously in a timed fashion well known to the art and supports a plurality of different type characters about its periphery. Document 16 is advanced, usually stepwise, in a manner also well known to the art and receives a series of character impressions on its upper surface as hammer 18 is actuated in proper timed sequence to print selected characters.

The hammer module includes hammer 18 which is supported at the end of a shaft 20 mounted for linear reciprocation in a pair of stationary guide plates 22 and 24 fixed to the machine frame. One side of hammer 18 is provided with a slot 32 which guides on a stationary pin 30 to prevent rotation of the hammer as the hammer moves up and down. A compression spring 26 is fitted over shaft 20 and retained between guide plate 24 and a retaining pin 28 fastened to shaft 20 so that the hammer and shaft assembly are normally biased downwardly in a non-printing position.

A solenoid core member 42 is fastened by means of a bolt 52 to the underside of upper guide plate 22. The core member 42 is made of a magnetic material such as Armco magnet iron and includes a primary pole piece 44, a secondary pole piece 45, and a stop bolt support extension 46. A solenoid coil 50 is wound around primary pole piece 44 and is connected in circuit with appropriate control circuit means 12. Circuit 12 transmits a current impulse to the coil each time it is desired to actuate hammer 18. Suitable circuits for supplying current impulses in proper timed relation with respect to rotation of the character drum are well known to the art and further description thereof is omitted since the drcuit plays no part in the present invention.

Secured to the lower left side of core member 42 is a non-magnetic pivot support member 35. Member 35 is slotted to pivotably support an actuating arm 34 which is connected to member 35 by pivot pin 36. Delrin (trademark) plastic has been found to be .a suitable material for the member 35. Actuating arm 34 carries a hemispherical stud 38 at its free end. Stud 38 engages the lower end of hammer shaft 20-. In its rest position, arm 34 is supported by head 56 of a stop bolt 54 which extends through an opening in arm 34 and is threadably attached to the support extension 46 of core member 42. A pair of damping washers surround bolt 54 and are located between head 56 and the upper surface of recess 3 40 in arm 34 into which the head fits. These damping washers are described in greater detail subsequently in connection with FIG. 2. A compression spring 58 is supported about bolt 54 between extension 46 and arm 34 and normally biases the arm downwardly in its rest position against the damping washers.

The space between the lower end of primary pole piece 44 and arm 34 determines the throw of the arm and for normal printing operations need be but a few thousandths of an inch. Secondary pole piece 45 is shorter than pole piece 44 and accordingly the major force of attraction on arm 34 is exerted by the primary pole piece. The stop bolt 54 is fabricated from a non-magnetic material such as #303 stainless steel so that arm 34 is magnetically separated from core member 42. Arm 34, of course, is made from magnetic material, such as Armco magnet lI'OIl.

Thus, when coil 50 is pulsed, arm 34 is drawn upwardly by the combined effect of a major force of attraction exerted by primary pole piece 44 and a minor force of attraction exerted by secondary pole pieces 45. This imparts upward movement to hammer shaft 20 and drives hammer 18 against document 16, causing the latter to be forced against ribbon 14 and character drum 10, creating a character impression on the document.

The distance between primary pole piece 44 and arm 34 is such that the arm contacts the pole piece and is arrested prior to the time that hammer 18 makes printing contact with the document surface. This means that hammer 18 is in free flight at the time it strikes the document.

By the time arm 34 has engaged pole piece 44, coil 50 has been de-energized by circuit 12 so that spring 58 immediately returns arm 34 to its rest position against the damping washers. The inherent rebound of hammer 18 from the print surface together with the action of spring 26 returns the hammer assembly to its rest position against stud 38.

Referring to FIG. 2, it is seen that the damping washers 61 and 62 are positioned one on top of the other whereby they eliminate a significant portion of the rebound oscillation which would result if the actuating arm were driven by spring 58 against the bare metal head 56. Good results are obtained by employing washers made of polyvinyl chloride of mils thickness each. The natural non-planar (lack of flatness) characteristics imparted to these washers in the course of their manufacture heightens the damping effect.

An important aspect of the invention, as previously discussed in general, lies in the fact that actuating arm 34 is acted upon substantially through its center of percussion. Thus, as shown in FIG. 1, the distance L between the center of pivot 36 and a line extended downwardly from the center of primary pole piece 44 should be fixed in accordance with the formula:

L=I ml where L=distance from pivot 36 to center of percussion I=rnoment of inertia of arm 34 about pivot 36 l=distance from pivot 36 to center of gravity of arm 34 m=mass of arm 34 Since the major force of attraction which is applied to arm 34 during the initial portion of a print cycle comes from primary pole piece 44 and is thus applied at the center of percussion of the arm, the arm experiences an almost pure rotational moment. This means that virtually no translational or linear components of force are applied to pivot 36 and substantially all the magnetic force of the solenoid is converted into movement of the hammer assembly. This also means that wear of pin 36 is minimized.

When arm 34 contacts pole piece 44, the reactionary force exerted thereby on the arm is also applied through the latters center of percussion. Again, translational forces transmitted to the pin 36 are at a minimum and additionally the noise generated by the impact at engagement is also minimized.

While the operation of the above described embodiment has already been brought out above, it is hereinafter briefly summarized. When the module is at rest, i.e., solenoid coil 50 is not energized, arm 34 is biased by spring 58 against damping washers 61 and 62 and hammer assembly 1820 is biased by spring 26 against stud 38. When coil 50 is pulsed, arm 34 is drawn upwardly about pivot 36 by the major force of attraction exerted by pole piece 44 and the minor force exerted by pole piece 45. This propels the hammer assembly upwardly against the bias of spring 26 and into printing contact with the surface of document 16. Prior to the time that the hammer makes printing contact, arm 34 is arrested by pole piece 44, and, the coil 50 having been deenergized, is returned to the rest position by spring 58. Shortly thereafter the hammer assembly is also returned to rest position by the combined effect of hammer rebound and bias force from spring 26.

While the embodiment described herein involves only a single print hammer and actuating arm, it is to be understood that a multi-hammer module may be fabricated by employing a single core member 42 machined to have a plurality of individual pole pieces 44 and 45, each of the former supporting an individual coil 50. An individual actuating arm 34 would be provided for each pair of pole pieces. In this manner a highly compact, side-by-side hammer arrangement can be obtained. It has been found possible to mount the hammers on 200 mil centers in accordance with the requirements of the most dense printing formats. With this kind of hammer spacing it is necessary to employ the offset print hammer arrangement described in U.S. Patent No. 3,306,191, assigned to the assignee of the present application, and to position the actuating units for alternating hammers on opposite sides of the hammer assembly. It is further to be understood that any type of movable type carrier such as a type chain or a reciprocating shuttle can be employed in place of the above described rotating drum.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the above as well as additional changes in form and details may be made therein without departing from the spirit and scope of the invention.

I claim:

1. A print hammer module comprising, in combination:

a substantially linearly movable print hammer positioned adjacent a print surface;

an actuating arm positioned substantially at a right angle to the direction of movement of said hammer, said arm being secured to a pivot at one end and having its other end in contact with said hammer; and

control means for selectively applying an actuating force to said arm to drive said hammer toward said print surface and for subsequently applying an arresting force to said arm, said means including a stop member having a stop surface positioned adjacent said arm for applying said arresting force thereto, the center of said stop surface being located the same distance from said pivot as the center of per cussion of said arm.

2. The print hammer module set forth in claim 1,

wherein said control means comprises:

a selectively operable solenoid having at least one pole piece positioned adjacent said arm, said solenoid, when energized, applying a magnetic actuating force to said arm.

3. The print hammer module set forth in claim 2 wherein said pole piece is positioned so that its center is substantially in line with the center of percussion of said arm whereby engagement of said arm with said pole piece causes an arresting force to be applied through the center of percussion of said arm.

4. The print hammer module set forth in claim 1, further comprising:

a frame;

a stop bolt threadably anchored to said frame and extending through an opening in said arm, said bolt terminating in a head positioned on a side of said arm away from said print surface; and

a compression spring surrounding said bolt and located between said frame and said arm to bias said arm toward said head.

5. The print hammer module set forth in claim 4, further comprising:

a damping washer surrounding said bolt and located between said arm and said head.

6 wherein:

said damping washer comprises two separate layers of polyvinyl chloride, each of said layers being nonplanar.

References Cited UNITED STATES PATENTS 2,787,210 4/1957 Shepard 101-93 2,940,385 6/1960 House 101-93 3,099,711 7/1963 Foley et a1. 197-1 X 3,177,803 4/1965 Antonucci 101-93 3,183,830 5/1965 Fisher et al, 101-93 3,200,739 8/1965 Antonucci a 101-93 3,306,191 2/1967 Sharples 101-93 6. The print hammer module set forth in claim 5, 15 WILLIAM B.PENN, Primary Examiner. 

